The present invention relates generally to semiconductor processing technology, and more particularly to a method for integrally forming a damascene gate structure and a resistive device on the same semiconductor substrate.
Radio frequency (RF) power devices require metal-oxide-semiconductor (MOS) transistors with gates of low sheet resistance. Such devices are typically used at frequencies between 900 MHz and 2 GHz for a wide variety of RF power amplifier applications, such as those in cellular handsets and telecommunication base stations. The low sheet resistance gate helps to provide large output power levels demanded by these applications. A damascene gate structure is typically used in such RF devices for lowering the sheet resistance. The damascene gate structure has a T-shaped cross-section with a top surface wider than its bottom surface. This wide top surface helps to reduce the sheet resistance of the gate structure.
An integrated circuit (IC) may include both the RF devices and other electronic elements that are used for a normal circuit operation. Some of the electronic elements may require a high resistance as opposed to the RF devices. For example, interconnects of one or more active regions on an IC chip typically require high resistance. This contradictory requirement of resistance poses a challenge to the IC manufacturing industry.
Therefore, desirable in the art of semiconductor processing technology are methods for integrally forming a damascene gate structure with a low sheet resistance and a resistive device with a high resistance on a semiconductor substrate.